Hearing aid



Sept 28, 1965 s. G. MCCARRELL ETAL 3,209,082

HEARING AID 6 Sheets-Sheet 1 Original Filed May 27, 1957 lNl/EN T 0R5dkml .WZ-fimd QW By 2%, MWM WM ATTORNEYS.

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HEARING AID 6 Sheets-Sheet 2 Original Filed May 27, 1957 @Wm mfl ATTORNEYS.

Sept. 1965 s. G. MCCARRELL ETAL 3,209,082

HEARING AID 6 Sheets-Sheet 3 Original Filed May 27, 1957 //.A I17 I28INVENTORS' ay fl W 91% ATTORNEYS.

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HEARING AID 6 Sheets-Sheet 4 Original Filed May 27, 1957 uvvavroes: g m.fid/nefl afld W BY W yfim ATTORNEYS.

Se t. 28, 1965 s. G. MGCARRELL ETAL 3,209,082

HEARING AID Original Filed May 27, 1957 6 Sheets-Sheet 5 QW 55 WATTORNEYS.

p 1965 s. G. MOCARRELL ETAL 3,209,082

HEARING AID Original Filed May 27, 1957 6 Sheets-Sheet 6 IN [/5 N TORSmm ATTORNEYS.

nited States This invention relates generally to hearing aids and moreparticularly to new and improved constructions for compact hearing aidswhich are adapted to be completely contained in the external ear. Thisapplication is a division of our co-pending application, Serial No.661,628, filed May 27, 1957, now Patent 3,061,689.

It is a general object of this invention to provide an improved hearingaid assembly in which all of the component parts are completelycontained in a composite unitary structure adapted to be worn in theexternal ear of the user.

It is another object of this invention to provide such a hearing aidassembly in which the microphone and receiver are positioned relativelyclose to each other, thus enabling the assembly to be reduced in size,but which are acoustically isolated from each other for enabling maximumavailable power and gain to be used with freedom from acoustical andvibratory feedback.

It is still another object of this invention to provide a hearing aidassembly having a receiver of unique construction which is adapted to beoperatively positioned within the ear canal closely adjacent the eardrum of the user.

It is a further object of this invention to provide sealing means aroundthe receiver within the ear canal for isolating the receiver from themicrophone to substantially eliminate acoustical and vibratory feedbacktherebetween.

It is a still further object of this invention to provide a novelresilient coupling member for coupling the receiver within the ear canalto the remainder of the hearing aid wherein the resilient couplingmember is constructed with sufficient stiffness to facilitate theinsertion of the receiver within the ear canal, yet with sufficientflexibility to fit the contour of the ear canal, especially duringmovement thereof as during talking, chewing and the like.

It is a still further object of this invention to provide a novelresilient coupling member, as described above, which serves not only tosupport the receiver in non-contacting relation with the ear canal butin addition serves to isolate the microphone from mechanical vibrationof the receiver to the end that such mechanical vibration is not fedback to the microphone.

Still another object of this invention is the provision of a compact,self-contained hearing aid assembly which is adapted to be containedwithin the external ear of the user and which, in an advantageousembodiment thereof, comprises a resilient coupling member adapted to fitwithin the ear canal for supporting a receiver closely adjacent the eardrum, and a front end control portion containing a microphone,amplifier, volume control, and battery, detachably coupled to theresilient coupling member and adapted to be mounted in the concha of theear so as to be substantially concealed from view.

It is still another object of this invention to provide a suitable earmold formed of a resilient material, such as plastic, rubber or thelike, which is adapted to enclose and support the front end controlportion of the hearing aid assembly and which further is adapted to beshaped as desired to fit into the ear of the user.

It is a still further object of this invention to provide a hearing aidassembly which comprises a subminiature atet O F 3,2fi9,082 PatentedSept. 28, 1965 volume potentiometer having a unique and advantageousconstruction.

A still further object of this invention is the provision of a new andcompact hearing aid assembly adapted to be fitted Within the ear, asdescribed above, and which comprises a compact yet high gain multi-stageamplifier circuit.

It is still another object of this invention to provide a new andimproved self-contained hearing aid assembly which is characterized byits unusually small size, its high sensitivity, and its freedom fromacoustical and vibratory feedback.

These and other objects are realized in accordance with a specificillustrative embodiment of this invention which comprises a subminiaturereceiver of unique construction adapted to be fitted deep into the earcanal adjacent the ear drum, a resilient coupling member housing thereceiver and serving to isolate the front end of the hearing aidassembly from mechanical vibratory feedback from the receiver, sealingmeans around the coupling member for providing an air-tight seal for thereceiver to prevent acoustical feedback therefrom to the microphone, acore supporting the microphone, amplifier, volume control and battery ofthe hearing aid assembly, and an ear mold of firm or resilient materialadapted for encasing the core and further adapted to be shaped forfitting the concha of the ear to the end that substantially the entirehearing aid assembly is concealed from view within the ear of the user.

In accordance with a feature of the invention, a preferred embodiment ofthe subminiature receiver comprises an annular non-magnetic outer sleevewhich carries therewithin an annular magnet, a centrally positionedcenter pole having a coil comprising a large number of turns of finewire wound therearound, an annular disc-shaped pole piece adjacent oneend of the magnet and having a central aperture through which one end ofthe center pole extends in closely adjacent relation to the pole piece,a special plastic diaphragm supporting a metal slug spaced from the polepiece and center pole for movement relative thereto in response to theenergization of the coil, and a non-magnetic cap positioned over thediaphragm and adapted to maintain the latter in proper operatingposition, the cap being provided with a centrally located hole having aninductance which cooperates with the trapped air between the diaphragmand the cap to provide a de sired acoustical response of the receiver.

In accordance with another feature of this invention, the spacingbetween th metal slug on the plastic diaphragm and the magnetic polesmay be adjusted as de sired to utilize maximum magnetic flux in thereceiver. Advantageously, the metal slug and the plastic diaphragm areconstrained between the outer sleeve and the cap, and the receiver coreand magnet assembly are magnetically adjusted relative thereto formaximum sound output and desired audio quality from the receiver. Itwill be appreciated by those skilled in the art that the uniqueconstruction of the receiver, as described above, enables the receiveroutput to be adjusted as desired without lowering the strength of themagnet itself in accordance with conventional prior art practices.

In accordance with another illustrative embodiment of the invention, thereceiver core and magnet assembly is encased in a plastic holding sleeveand the plastic diaphragm is held in position adjacent the magneticpoles by means of a plastic cap fitted over the edges of the diaphragm.Advantageously, a loose plastic protective cover is provided at thecentral portion of the plastic cap to prevent dirt, wax and otherforeign elements from enter ing the receiver.

In accordance with further features of this invention, additionalembodiments of subminiature receivers adapted to be fitted within theear canal are provided including a receiver having the coil concentratedat the gap end of the core which utilizes the leakage flux by causing itto be circulated at the gap, a receiver having its magnet centrallydisposed therein with its coil wound adjacent the pole pieces at theinner surface of the outer sleeve, and a receiver having its diaphragmlongitudinally disposed within the outer sleeve and extendingsubstantially the length thereof.

Still further features of this invention include subminiature receiversfor use within the ear canal which comprise a receiver of thepiezo-electric type having a crystal transducer, such as bariumtitanate, and a diaphragm positioned in an outer sleeve, as describedabove, and a dynamic receiver having a moving coil fastened to thediaphragm and positioned between opposite pole pieces within the outersleeve.

Acoustical feedback from the receiver within the ear canal to themicrophone is prevented in accordance with a feature of this inventionby means of a plurality of thin sealing members spaced along the outersurface of the receiver housing. These thin sealing members engage theinner wall of the ear canal to provide an air-tight seal between thereceiver output and the front end control portion of the hearing aidassembly. The isolation att ained by this novel arrangement effectivelyresolves the problem of acoustical feedback which normally would bepresent due to the close proximity of the microphone and receiver andthereby makes possible the use of maximum attainable gain from theamplifier of the hearing aid, It

will .be appreciated that the increased sensitivity thus permittedtogether with the increased sensitivity provided by placing the receiverwithin the ear canal adjacent the ear drum represent a significantadvance in the hearing aid art.

The resilient coupling member which connects the receiver to the frontend control portion of the hearing aid advantageously is in the form ofa hollow tube through which the conductors for energizing the receiverare positioned. In accordance with the invention, the longitudinalrigidity of the coupling member is suflicient to permit the receiver tobe inserted within the ear canal Without permitting undue vibratoryfeedback from the receiver. Further, the resilient coupling member isconstructed with sufficient flexibility to follow the contour of the earcanal while the latter is both at rest and in motion as during talking,eating and the like.

The resilient coupling member advantageously is detachably coupled tothe compact high gain amplifier circuit which in accordance with afeature of this invention comprises a multi-stage transistor circuithaving both positive and negative feedback characteristics and, further,which is characterized by the elimination of audio couplingtransformers. A volume control potentiometer of novel construction isincluded in the amplifier circuit, and in accordance with a feature ofthis invention, the volume control potentiometer comprises asubminiature barrel of insulating material having a resistance stripprovided along the inner surface thereof, and a helical contact wire,movable with respect to the barrel and adapted to contact the resistancestrip at a different single point for each operative position of thebarrel and contact wire.

It is a further feature of this invention that the microphone,amplifier, volume contr-ol potentiometer and battery which comprises thefront end control portion of the hearing aid assembly be mounted in asuitable mold of plastic, rubber or the like, which is shaped to fit theconcha of the ear of the user. Advantageously, the battery is mounted ina recessed hinged holder which is adapted to be pulled out of the earmold for facilitating the insertion and replacement of the batterytherein.

The above and other features of novelty which characterize the inventionare pointed out with particularity in the claim annexed to and forming apart of this specification. For a better understanding of the invention,and

its advantages, reference is had to the accompanying drawing anddescriptive matter in which is shown and described several illustrativeembodiments of the invention.

In the drawing:

FIGURE 1 is a perspective view of a hearing aid assembly embodyingprinciples of the invention;

FIGURE 2 is a drawing illustrating the embodiment of FIGURE 1 inoperative position within the external ear of the user;

FIGURE 3 is a plan view in cross section of the front end controlportion of the hearing aid assembly;

FIGURE 4 is a perspective view of the front end control portion of thehearing aid assembly illustrating one embodiment of a recessed batteryholder;

FIGURE 5 is a perspective view of one illustrative form of resilientcoupling member embodying the invention;

FIGURES 6 through 10 are cross sectional views of several illustrativeresilient coupling members in accordance with the invention;

FIGURE 11 is a view, partly in cross section, illustrating theconstruction of the coupling element electrical contact assembly;

FIGURES 12 through 22 are views illustrating the construction of severalsubminiature receivers embodying principles of the invention;

FIGURES 23 through 27 are views illustrating the construction of severalsubminiature volume control potentiometers in accordance with theinvention;

FIGURE 28 is a schematic diagram of a multi-stage transistor amplifiercircuit in accordance with the invention;

FIGURE 29 is a cross sectional view of a directly coupled embodiment ofsubminiature receiver;

FIGURES 30 and 31 are views illustrating a hydraulically coupledembodiment of the receiver in accordance with the invention; and

FIGURE 32 is an enlarged partial view of the plastic diaphragm assemblyutilized in certain embodiments of the invention showing the diaphragmconstruction in greater detail.

Referring now to the drawing and more particularly to FIGURES 1 through5 thereof, there is shown a specific illustrative embodiment of hearingaid assembly embodying the invention which comprises a receiver portion10 adapted to be inserted within the ear canal of the user and a frontend control portion 12 adapted for operative connection to the receiverportion 10 and further adapted to be fitted into the concha of the earof the user. Advantageously, receiver portion 10 comprises an elongatedtubular housing 14 through which conductors 15 and 16 extend and havinga subminiature receiver 18 mounted at one end thereof.

In accordance with an aspect of this invention, tubular housing 14 isformed of a resilient and flexible material, such as rubber or plastic,to the end that the receiver portion 10 is made to follow the contoursof the ear canal 17 when the receiver portion 10 is operativelypositioned therein as shown in FIGURE 2. Further, as explained ingreater detail hereinbelow, tubular housing 14 is formed with suflicientlongitudinal rigidity to facilitate the insertion of the end containingthe subminiature receiver 18 into operative position within the earcanal adjacent the ear drum 19.

It will be appreciated by those skilled in the art that in prior arthearing aids in which the receiver was mounted near the microphoneserious problems arose as a result of the acoustical or vibratoryfeedback therebetween. Thus, it often became necessary in the prior artto reduce the gain of the amplifier used in the hearing aid to minimizesuch acoustical feedback. The construction of the present inventionenables the use of a full gain amplifier despite the close proximitybetween the receiver 18 and the microphone 37 due to the positioning ofthe receiver 18 within the ear canal and to the provision of acousticalsealing members 20 and 22 extending outwardly from tubular housing 14into engagement with the walls of the ear canal. Sealing members 20 and22, which are formed from a suitably resilient material, serve not onlyto provide an air tight chamber for the receiver, but in addition serveto compensate for variations in diameter of the ear canals of thevarious users of the invention.

The front end control portion 12 of the hearing aid assemblyadvantageously is housed in an ear mold or assembly 28 which preferablyis formed of a suitable material, such as plastic or rubber, and isadapted to be seated into the concha 30 of the ear of the user. Ear mold28 has positioned therein a source of power for the hearing aid in theform of a subminiature battery 21 which in one embodiment of theinvention is positioned in a recessed holder 32.. To facilitate theremoval and replacement of battery 31, holder 32 is pivoted, such as atpivot 33, so as to be fitted into a slot 34 provided in the mold 28 whenthe battery is in position and to be pulled out from the mold 28 duringremoval or replacement of the battery.

Ear mold or assembly 28 also has positioned therein a microphone 37which is mounted so that its pick-up opening 38 is in alignment with asuitable opening 42 at the front of ear mold 28. An-amplifier 39 ispositioned adjacent microphone 37 and in accordance with the preferredembodiment of the invention, as described in detail below, amplifier 39is a multi-stage amplifier circuit comprising suitably connectedtransistors 40 and resistance and capacitance elements 41.

The amplifier circuit also is provided with a volume control and on-otfswitch which advantageously may be in the form of a subminiaturepotentiometer 35 having a manually operable control knob 36 extendingtherefrom into manually accessible position outside the ear mold 48. Itis a feature of this invention that the amplifier, microphone, volumecontrol and battery may be assembled on a flexible form which isinserted into a special ear mold, or alternatively, the ear mold may beformed around this package to provide a custom fit.

The receiver portion and the front end control portion 12 of the hearingaid assembly are made detachable from each other to permit customfitting of the ear mold 28 to the ear of the user as well as tofacilitate maintenance and repair of the front end control portion. Inaccordance with a feature of this invention, the subminiature receiver18 is electrically connected to the amplifier 39 by means of conductorsand 16 which terminate in the coaxial connectors 27 and 26 adapted toplug into the amplifier when the receiver portion 10 and front endcontrol portion 12 are operatively connected.

This connection is facilitated by means of an eccentric flange 24 havinga finger grip 25 provided at one end of a tubular housing 14 of thereceiver portion 10. It can be seen, as for example from FIGURES 1, 2and 3, that when receiver portion 10 and front end control portion 12are connected together, the rearward portion of the ear mold 28 isseated against the eccentric flange 24 to provide an effectiveconnection therebetween.

In accordance with features of this invention, the tubular housing 14may take several forms. The criterion which must be met, however, isthat .the tubular housing 14 have suflicient rigidity in thelongitudinal direction to permit the subminiature receiver 18 at one endof the housing to be readily inserted into the ear canal closelyadjacent the ear drum plus suflicient flexibility in the transversedirection to permit the tubular housing 14 to follow the contours of theear canal both when the canal is in its static condition and while it isin motion such as during talking, chewing, and the like.

Accordingly, there is shown in FIGURE 6 a prefrfre d construction oftubular housing having a vertebrate joint construction in which aplurality of wafers 43 of a relatively soft material such as foam rubberare provided at spaced intervals along the housing body 44. Since the 6housing body is formed of a stiffer and less resilient material, such ashard rubber or plastic, it will be appreciated that this constructionenables flexible bending of the housing to be obtained with a maximumlongitudinal rigidity and also a minimum longitudinal sound conduction.

The tubular housing embodiment shown in FIGURES 7 and 7A comprises abody 45 of a relatively soft material which serves to substantiallylessen unwanted conduction transmission in a longitudinal directionalong the housing from the receiver 18 to the front end control portion.The use of the soft material for the housing body 45 is enabled by thesemi-flexible rod or stiffener 46 shown in FIGURE 7A. Thus to insert thereceiver portion within the ear canal, flexible rod 46 is positioned bymeans of the finger grip 47 within the molded hole 48 provided thereforin the housing body 45. During the insertion operation, semi-flexiblerod 46 adds suflicient longitudinal rigidity to the tubular housing toenable the latter to be properly placed within the ear canal withoutbuckling as would be the case if the rod 46 were not used. Manifestly,after the tubular housing is in place within the ear canal, thesemi-flexible rod 46 may be removed to reduce unwanted conductiontherethrough as well as to gain the transverse flexibility inherentlyobtainable from the soft material comprising the housing body 45.

A further preferred construction for the tubular housing of the receiverportion 10 is shown in FIGURE 8 wherein the tubular housing 46 takes theform of a connecting tube having a beaded shape. Thus, the connectingtube is formed of a resilient material having a plurality of beadedportions 47 spaced along the length thereof to provide the longitudinalrigidity and transverse flexibility required, as described above.

In the illustrative tubular housing embodiment shown in FIGURE 9, thehousing 14 is provided with an elongated annular hollow portion 23intermediate the outer surface of the housing body and the centralconductor tube. In accordance with an aspect of the invention, hollowportion 23 is filled with a wax, gelatinous material or any suitablethermoplastic material that will become more pliable with heat. Thus,the fill material in hollow portion 23 oflers sutficient rigidity duringinsertion of the receiver portion 10 into the ear canal and with thesubsequent loosening of the fill material due to body heat, the tubularhousing 14 becomes flexible, as desired. Manifestly, other constructionsfor the tubular housing 14 equivalent to the constructions shown inFIGURES 6, 7, 8 and 9 may be utilized in accordance with the inventionprovided the necessary combination of longitudinal rigidity andtransverse flexibility are present.

Referring back to FIGURE 8, there is illustrated one way in which thesubminiature receiver 18 may be mounted within the tubular housing 46 ofthe receiver portion 10. Thus, the tubular housing body 46 is enlargedat one end for receiving and completely enclosing the subminiaturereceiver 18. Advantageously, the enlarged portion 48 of the tubularhousing 46 is provided with a circular fin or acoustical sealing member49 extending out- Wardly around the enlarged portion 48 for providing anair tight seal in the ear canal to prevent acoustical feedback from thereceiver 18 to the microphone 37 infront control portion 12. Anadditional sealing member 50 is provided at the end of the enlargedportion 48 of tubular housing 46 to further reduce the acousticalfeedback and to provide a cushion for the subminiature receiver 18Within the ear canal to the end that the inner surface of the ear canalas well as the ear drum is cushioned from the receiver.

It will be appreciated by those skilled in the art that in accordancewith the principles of this invention, a plurality of circular fins orsealing members may be provided in spaced relation along the enlargedportion 48 of the tubular housing surrounding the receiver 18 as shownin FIGURES 9 and 10. In addition, the receiver portion 10 may beconstructed in the form of a single integrally constructed tubularhousing and eccentric flange as shown in FIGURES 8 and 9 or in the formof a composite unitary connection such as the three element constructionof FIGURE 10. Thus, it can be seen in FIGURE 10 that the eccentricflange 24 is individually formed and is connected to the one end of thetubular housing 14. The other end of the tubular housing 14 is connectedto a separately constructed receiver housing 48. Other equivalentconstructions for the tubular housing 14 are fully within the spirit andscope of this invention.

The manner in which the receiver 18 is connected to the coaxialconnector contacts 26 and 27 is shown in detail in FIGURE 11 of thedrawing. Thus, in accordance with a specific illustrative embodiment ofthe invention, the terminals 50 and 51 for the coil 52 of the receiver18 are connected by means of conductors and 16 respectively to thecoaxial connector contacts 26 and 27. Advantageously, coil terminals 50and 51 are formed on a printed circuit disc 53 secured to the end of thereceiver housing. Coil terminal 50 is connected by conductor 15 to thecoaxial conductor 26 and coil terminal 51 is connected by conductor 26to the coaxial conductor sleeve 27. A suitable insulating sleeve 54 isprovided between the contacts 26 and 27.

A preferred embodiment of receiver 18 is shown in FIGURE 12 of thedrawing. Advantageously, this receiver comprises a housing or outersleeve 55 of a nonmagnetic material, such as non-magnetic stainlesssteel, which has positioned therewithin an annular magnet 56 having acenter pole 57 secured at one end thereof. The base 58 of center pole 57is sandwiched between the one pole of magnet 56 and the printed circuitdisc 53, which as explained above, has conductor terminals 50 and 51secured thereto. The opposite pole of magnet 56 has a disc shapedannular pole piece 59 secured thereto and the central elongated portion60 of center pole 57 extends into the aperture defined at the center ofannular pole piece 59.

A coil 61, which advantageously comprises a large number of turns ofrelatively fine wire, is wound around the central portion 60 of centralpole 57 in operative association therewith and the ends of coil 61 areconnected to the printed circuit disc terminals 50 and 51. Suitableopenings 62 are provided at the base portion 58 of center pole 57 and inthe printed circuit disc 53 for enabling the coil ends to be connectedto their terminals. If desired, suitable damping means such as dampingmember 64 may be provided around the central portion 60 of center pole57 adjacent the pole piece 59.

In accordance with an important aspect of this invention, thesubminiature receiver 18 is provided with a special plastic diaphragm 65described in detail below. A metallic slug 66 is secured to the plasticdiaphragm 65 with a suitable adhesive and is positioned relative to thepole piece 57 so as to be responsive to the energization of the latterby coil 61. A cap 67 of a non-magnetic material, such as non-magneticstainless steel, is formed With an enlarged flange portion 68 to the endthat when the cap 67 is fitted in proper position over the receiverouter sleeve 55, the flange portion 68 of cap 67 cooperates with theouter sleeve 55 to hold the plastic diaphragm 65 tightly stretched overthe center pole 60 and pole piece 59.

Advantageously, the receiver 18 may be assembled by placing a plasticdisc 65 with the slug 66 attached thereto over the end of outer sleeve55. Cap 67 then is pressed over the plastic disc 65 until the shoulderof the flange portion 68 of cap 67 is properly seated against the outeredge of outer sleeve 55.

In accordance with a feature of this invention, the position of slug 66relative to magnet 56 may be mechanically adjusted to utilize maximummagnetic flux without requiring the magnet to be knocked down. Thus, theplastic diaphragm 65 is held tightly stretched over magnet 57 by cap 67,as described above, and the magnet and coil assembly is adjustedrelative to plastic diaphragm 65 and metal slug 66 from the other end ofouter sleeve 55 until the desired spacing is attained. It will beappreciated by those skilled in the art that this desired spacing may beattained by adjusting the magnet and coil assembly within the outersleeve for a maximum sound output and desired audio quality from thereceiver. After this adjustment is completed, the positions of themagnet and coil assembly, and of the cap relative to the outer sleevemay be fixed by any suitable means such as an adhesive.

The cap 67 is provided with a central aperture 69 which is of a diametersuch that the trapped air within the receiver 18 and the inductance ofaperture 69 provides maximum acoustical response. It now is understoodthat the receiver 18, despite its extremely small parameters, is adaptedto provide etfective transmission of audio signals to the ear drum.

The size of the subminiature receiver 18 may be appreciated in that inan illustrative embodiment constructed in accordance with the abovedescription, the overall length was .230 inch, the overall diameter was.200 inch and the spacing between the pole piece and the spacing betweenthe magnetic coils and the plastic diaphragm was adjusted a distance of.010 inch. It further will be understood that the use of the plasticdiaphragm 65 in a subminiature receiver enables the attainment ofsatisfactory acoustical response in a receiver having such relativelysmall dimensions.

In accordance with a preferred construction of the subminiature receiver18, the plastic diaphragm is formed in the manner shown in FIGURE 32. Asdepicted therein, the diaphragm 65 comprises two layers of plastic film180 and 181, respectively, which are held together by a layer ofsuitable adhesive 182, sandwiched between layers 180 and 181.

In an illustrative plastic diaphragm constructed as shown in FIGURE 32,the plastic film layers 180 and 181 advantageously were formed of mylarand the film layer 181 was coated with vaporized aluminum coating 183 toadd additional stifiness to the diaphragm. It will be appreciated bythose skilled in the art that other constructions and materials for theplastic diaphragm 65 may be utilized with desirable results in lieu ofthe illustrative construction shown in FIGURE 32 and that the use ofsuch alternative forms are within the spirit of the invention.

Another illustrative embodiment of subminiature receiver 18, as shown inFIGURE 13 of the drawing, comprises an outer sleeve 70, advantageouslyformed of a plastic material, which has mounted therewithin an annularmagnet 56 having a center pole 60 and a pole piece 59, and a coil 61wound around the center pole 60 in the manner described above. A plasticdiaphragm 65 having a metallic slug 66 positioned thereon is heldtightly stretched over magnet 57 by means of a plastic cap 71 seatedagainst the plastic outer sleeve 70 to the end that the plasticdiaphragm 65 is held between the plastic sleeve 70 and cap 71, and themagnetic pole piece 59. Advantageously, pole piece 59 may have a raisedportion 72 extending therearound adapted to cooperate with the inneredge of the plastic cap 71.

In accordance with a feature of this embodiment, plastic cap 71 isprovided with a suitably dimensioned central opening across which ispositioned a loose plastic protective cover 73. Protective cover 73serves to keep foreign elements such as dirt, wax, etc. from enteringthe receiver 18 and at the same time permits effective soundtransmission therethrough to the ear drum.

In a further illustrative embodiment of subminiature receiver 18, asshown in FIGURE 14 the annular magnetic pole piece 75 serves as theouter sleeve of the receiver. A nonmagnetic sleeve 76 is positioned overa portion of pole piece 75 and a non-magnetic cap 67 is seated oversleeve 76 to the end that the plastic diaphragm 65 upon which metallicslug 66 is afiixed, is held tightly stretched over the magnet centerpole 77. In this embodiment of receiver 18, the magnet 78 isconcentrated at one end of the receiver cavity and the coil 79, to whichthe audio signals are applied from the hearing aid amplifier, is woundin concentrated form over the central pole 77 at the other end of thereceiver cavity. The construction shown in FIGURE 14 has the advantageof utilizing the leakage flux. It will be appreciated by those skilledin the art that the utilization of leakage flux in this manner serves toincrease the magnetic flux variations in the gap and thus increase thereceiver efiiciency.

Another illustrative embodiment of receiver 18 is shown in FIGURE 15 ofthe drawing. This embodiment is similar in some respects to thesubminiature receiver embodiment shown in FIGURE 12 with the exceptionthat the coil of wire 80 for receiving the audio signals from theamplifier is wound in the form of an annular coil adjacent the innersurface of the shell 81 of the receiver. This is in contrast to theconstruction of FIGURE 12 in which the coil 61 is wound around thecenter pole 60. Thus, in the embodiment of FIGURE 15, the magnet 82 maybe formed with relatively greater cross section and further may extendfrom the printed circuit disc 53 to a position closely spaced from theplastic diaphragm 65. The sub-miniature receiver shown in FIGURE 15 hasthe advantage in being simpler and cheaper to build than theconstructions of the other illustrative embodiments described above.

Still another illustrative embodiment of subminiature receiver is shownin FIGURES 16, 17, and 18 of the drawing. In this construction thenon-magnetic outer sleeve 83 has positioned therewithin an elongated U-shaped magnet 84 which extends substantially the entire length of thereceiver. An elongated center pole 85 and coil 86 are positioned in theU-shaped magnet 84 and also extend substantially the length of thereceiver. A plastic diaphragm 87 and metal slug 88 positioned thereonare placed over the U-shaped magnet 84 and held tightly stretchedthereacross in closely spaced relation to center 'pole 85 by means ofthe outer sleeve 83. It will be appreciated that this constructionenables the area of the diaphragm to be considerably enlarged over thediaphragm areas of the receiver constructions described heretofore. Oneend of the outer sleeve 83 is sealed as by means of the printed circuitdisc 53 and the sound pressure, which is considerably greater due to thegreatly enlarged area, is transmitted to the ear drum from the other endof the receiver. 7

In the illustrative receiver embodiment shown in FIG- URE 19 of thedrawing, the outer tube or sleeve 90 has positioned therewithin a tube91 of ceramic material which advantageously may be barium titanate. Adiaphragm 92 is positioned between ceramic tube 91 and the outer sleeve90, and is stretched across one end of the outer sleeve 90 to seal thelatter by the gripping effect of the outer sleeve in cooperation withthe ceramic tube 91. Conductors 15 and 16 from the amplifier in thefront end control portion of the hearing aid assembly are connected toopposite surfaces of the ceramic tube 91 for causing the latter tovibrate diaphragm 92 in accordance with the audio signals.

If desired, substantially greater output may be obtained by the use ofthe ceramic receiver construction shown in FIGURES 20 and 21. In thisillustrative embodiment, a bar 93 of ceramic material, whichadvantageously may also be barium titanate, is mounted on a supportmember 94 so as to extend longitudinally within the outer sleeve 95. Adiaphragm 96 is mounted in a rectangular frame 97 supported by a pair oftransverse end members 98 so as to also extend along the length of thereceiver. Diaphragm 96 is operatively connected to the ceramic bar 93 bymeans of a linking connector 99, and the audio signal conductors 15 and16 are connected to opposite surfaces of the ceramic bar 93 to the endthat ceramic bar 93 re- 1Q sponds to the signals to cause diaphragm 96to vibrate at a frequency corresponding to the frequency of the signals.

One end of the receiver outer sleeve is sealed by a wall 100 and theother end of the receiver is provided with a suitable opening throughwhich the sound pressure resulting from vibration of diaphragm 96 istransmitted. The vibratory action of diaphragm 96 is facilitated inaccordance with an aspect of this invention by means of the peripheralcorrugations 101 provided at the marginal portions of the diaphragmadjacent the rectangular frame 97.

In a still further illustrative embodiment of subminiature receiverwhich may be utilized in the hearing aid assembly of the invention, asshown in FIGURE 22, one pole of a magnet 102 is afiixed to the end wall103 of a magnetic shell 104. A center pole 105 is secured to the otherpole of magnet 102 and an annular pole piece 106 is secured to the shell104 in spaced relation with center pole 105 so as to define a gaptherebetween.

A printed circuit disc 53 is attached to the outer surface of end wall103 and carries thereon a pair of terminals 50 and 51 to whichconductors 15 and 16 from the amplifier of the hearing aid may beconnected. Terminals 50 and 51 are connected by means of conductors 107and 108 to an annular moving coil 109 positioned in the annular gapdefined by pole piece 106 and center pole 105. Moving coil 109 is heldin position in the gap and is enabled to vibrate longitudinally thereofin response to audio signals by means of a resilient diaphragm 110secured at its edges to the outer edges of shell 104. Thus, it will beappreciated that the subminiature receiver of the invention may take theform of a moving coil type of a dynamic receiver as well as the magneticand ceramic forms described above.

The volume control potentiometer 35 mounted within the ear mold 28advantageously may be constructed as shown in FIGURES 23 and 24 of thedrawing. As shown therein, the potentiometer 35 comprises a cylindricalbarrel formed of an insulating material and having a strip of resistancematerial 116 positioned along the inner surface thereof and extendingsubstantially the entire length of the barrel 115. A shaft 117 isrotatably mounted in a pair of metal bushings 118 and 119 respectively,at opposite ends of the barrel 115 and in electrical contact withresistance strip 116. Advantageously, suitable insulating members suchas insulating rings 120 and 121 and insulating discs 120a and 121a areprovided between metal bushings 118 and 119 and shaft 117, and the shaft117 is held in position within the barrel by means of the C-rings 122and 123. One resistance strip terminal 124 is provided between bushing118 and barrel 115, and the other resistance strip terminal 125 isprovided between bushing 119 and barrel 115. The wiper terminal 126 forthe potentiometer is connected to a metal clip member 127 which is inelectrical contact with one end of the shaft 117.

In accordance with the invention, the potentiometer wiper comprises ahelical contact wire 128 which is positioned around shaft 117 and whichis connected at one end thereof to the shaft adjacent the bushing 120and at the other end thereof to the shaft adjacent the bushing 121. Thediameter of helical contact wire 128 is such that the wire engages theresistance strip 116 at one point thereof for each position of the shaft117 relative to the barrel 115. Thus, in the operation of thepotentiometer 35, the output resistance may be varied as desired in arelatively simple manner by rotation of the shaft 117 within barrel 115.Manifestly, a manually operable control knob 126, as shown in FIGURES 1through 4 for example, may be connected to shaft 117.

. 117 may be substantially cup-shaped to the end that a suitable brushcontact 131 may be secured to the inner surface thereof, as by means ofthe rivets 132 extend through the wall of knob 130. The outer surface ofbarrel 115 has a suitable on-off circuit printed thereon in the form ofthe conductor 133 extending around barrel 115 and connected to terminal134, and conductor 135 extending around barrel 115 and connected toterminal 136. It can be seen that the rotation of knob 130 with respectto barrel 115 enables the circuit between terminals 134 and 136 to beopened and closed, as desired, to energize the hearing aid assembly fromthe battery 31. Advantageously, the range of rotation of knob 130 may bedefined by a pair of cooperating limit stops 129 and 143, provided onknob 130 and barrel 115, respectively.

In an alternative construction for the hearing aid potentiometer, asshown in FIGURE 27, the shaft 117 is fixed to a suitable support 138, asby means of pins 139 and 140 at opposite ends of shaft 117, and thebarrel 115 is made rotatable with respect to the fixed shaft 117 toprovide the desired sliding contact between helical contact wire 128 andthe resistance strip 116 on barrel 115. In this embodiment, it will beappreciated that suitable bushings such as bushings 141 and 142, areprovided for the rotatable barrel to facilitate rotation of the latterwith respect to the fixed shaft 117.

Those skilled in the art will readily appreciate that the novel featuresdescribed above with respect to FIGURES 23 through 27 enable thepotentiometer to be constructed in a subminiature yet efficient mannersuitable for the requirements of the compact hearing aid assemblydescribed herein.

A specific illustrative circuit suitable for the hearing aid assembly ofthe invention is shown in FIGURE 28. In this preferred embodiment, athree stage high gain transistor amplifier is connected between themicrophone 37 and the receiver 18. The use of a high gain amplifier fora hearing aid in which the microphone is positioned so near to thereceiver is unique with this invention and is made possible by thepositioning of the receiver within the ear canal adjacent the ear drumtogether wtih the sealing fins surrounding the receiver to preventacoustical feedback by the receiver to the microphone, as described indetail hereinabove.

In the amplifier circuit shown in FIGURE 28, one microphone terminal isconnected to the base electrode 144 of transistor 145, the collectorelectrode 146 of which is connected to the negative terminal of battery31. The emitter electrode 147 of transistor 145 is connected through aresistance 148 and the on-ofi" switch 149 to the positive terminal ofbattery 31. Emitter electrode 147 of transistor 145 also is connected tothe base electrode 150 of transistor 151.

The emitter electrode 152 of transistor 151 is connected through theparallel combination of resistance 153 and capacitance 154, and switch149 to the positive terminal of battery 31. The collector electrode 155of transistor 151 is connected through a capacitance 156 to the baseelectrode 157 of transistor 158. Emitter electrode 159 of transistor 158is connected through a resistance 160 and switch 149 to the positiveterminal of battery 31. The collector electrode 161 of transistor 158 isconnected through a resistance 162 to the base electrode 157 and to aterminal of the receiver 18.

The resistance strip 116 of the volume control potentiometer 35 isconnected between the other terminal of receiver 18 and the connectorelectrode 155 of transistor 151. The helical contact wire 128 ofpotentiometer 35 is connected through a resistance 163 to the otherterminal of microphone 37.

It can be seen that the on-off switch 149 and the helical contact wire128 of the potentiometer 35 are mechanically coupled, as describedabove, to the end that the electrical gain and output volume of thehearing aid assembly may be controlled by a single manually controlledknob. In accordance with an aspect of this invention, fidelity ofreproduction is attained from the three stage transistor amplifier bymeans of a negative feedback resistance 164 connected between theemitter electrode 159 of transistor 158 and a terminal of microphone 37.Additionally, a capacitance 165 is connected between negative feedbackresistance 164 and emitter electrode 147 of transistor 145. Further, apositive feedback resistance 165 is connected between a terminal ofreceiver 18 and a negative terminal of battery 31. The junction ofpositive feedback resistance 165 and the negative terminal of battery 31also is connected to an intermediate point in the potentiometerresistance strip 116 and to the collector electrode 146 of transistor145.

In accordance with a feature of this invention, both positive andnegative feedback is provided in the three stage transistor amplifiercircuit by feeding the signal output from the third transistor stageback to the input of the first transistor stage. Thus, the positivefeedback is provided by feeding back from the output of transistor 158an in-phase signal to the microphone input of transistor and thenegative feedback signal is provided by feeding back from the transistor158 an out-of-phase signal to the microphone input of transistor 145. Inaccordance with this specific illustrative embodiment of the invention,the positive feedback signal is taken from the collector electrode 161of transistor 158 at the receiver 18 and is applied through the positivefeedback resistance to the potentiometer resistance 116. Thepotentiometer wiper 128 serves to feed back this positive feedbacksignal to the microphone input of transistor 145 through the resistance163. The negative feedback is provided by taking a negative feedbacksignal from the emitter electrode 159 of transistor 158this emitterelectrode signal being out of phase with the collector electrodesignal-and applying this negative feedback signal to the microphoneinput of transistor 145 through the negative feedback resistance 164.Accordingly, it can be appreciated that the two out-of-phase signalsobtained at the transistor 158 are fed back to the input of theamplifier to provide greater fidelity of reproduction.

It will be readily understood by those skilled in the art that, ifdesired, transistors of opposite P-N characteristics may be used inplace of the transistors shown in FIGURE 28 by reversing the connectionsof the battery 31.

An illustrative embodiment of a directly coupled subminiature receiveris shown in FIGURE 29 of the drawing. In accordance with the invention,the directly coupled receiver comprises an outer shell 170, formed of anon-magnetic material, and having an annular magnet 180 with a centerpole 171 positioned therewithin. A coil 172 is wound around the centerpole 171 and the ends of the coil are connected to the terminals 50 and51 secured to the printed circuit disc 53 in the manner describedheretofore. The receiver is completely enclosed by a tubular housing 10of resilient material having a front wall 173, advantageously formed ofsoft rubber or the like, adjacent the pole piece 174 and center pole 171of the magnet 180. The tubular housing 10 is provided with suitableoutwardly extending fins 175 which serve to form a sound seal and airtrap to prevent acoustical feedback in the ear canal as describedhereinabove.

It is a feature of this embodiment that the diaphragm responsive to theenergization of coil 172 by the audio signals from the amplifier islocated outside of the receiver housing proper in contrast to theconstructions of the receivers described above. In this embodiment amagnetic slug 176 is afiixed directly to the ear drum 19 to the end thatthe magnetic slug 176 and ear drum 19 are vibrated directly inaccordance with the audio signals. It will be appreciated that as aresult of this direct coupling between slug 176 and ear drum 19, greaterefficiency and response can be attained from the receiver. It will beunderstood by those skilled in the art that to prevent possible injuryto the ear drum, the magnetic slug may be plastic coated and secured tothe ear drum 13 by known adhesive materials which are not injurious tothe ear drum.

A hydraulically coupled receiver embodiment is shown in FIGURES 30 and31 of the drawing. It is known that the efiiciency of sound transmissionis much greater when the sound is transferred through a hydraulic mediumthan when the sound is transferred through an air medium inasmuch as thelatter is compressible and the former is not. Thus, in accordance withthe invention, the sound transmission is maximized from the subminiaturereceiver 18 by the provision of a hydraulic medium between the receiver18 and the ear drum 19.

In FIGURE 30, there is shown a cotton wad 177 which advantageously maybe saturated with a suitable liquid such as a boric acid ointment.Cotton wad 177 is positioned adjacent the receiver 18 and is placed incontact with the ear drum 19 to the end that sound transmission from theformer is effectively communicated to the ear drum.

A further illustrative embodiment of a hydraulic coupled receiver isshown in FIGURE 31 in which the receiver 18 is provided with a tubularhousing having a plurality of sealing fins 178 extending therefrom intohermetically sealed contact with the walls of the ear canal. The spacebetween the end of the receiver 18 and the ear drum 19 is filled with asuitable fluid, which advantageously may be a silicone liquid, such thatthe audio output of the receiver 18 is transmitted through the liquid ina highly efficient manner to the ear drum 19. It will be appreciated bythose skilled in the art that various other means for providinghydraulic coupling between the receiver and the ear drum may be devisedin accordance with the teachings of this invention.

It will be understood by those skilled in the art that changes may bemade in the construction and arrangement of the parts of theillustrative embodiments of the hearing aid assembly disclosed hereinwithout departing from the real spirit and scope of this invention andthat it is intended to cover by the appended claim any modified forms ofstructures or use of equivalents which may reasonably be included withintheir scope.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

A compact hearing aid assembly comprising a receiver adapted to befitted within the ear canal and closely adjacent the ear drum of theuser, a front end control portion adapted to be fitted into the conchaof the ear, conductor means connecting said front end control portion tosaid receiver, and resilient coupling means for enclosing said conductormeans and said receiver, said resilient coupling means comprising anelongated tubular member having a body of relatively stifi resilientmaterial and a plurality of relatively soft resilient joints at spacedintervals along said body to enable flexible bending of said tubularmember together with a desired longitudinal rigidity.

References Cited by the Examiner UNITED STATES PATENTS 1,559,597 11/25Williams 179117 2,487,038 11/49 Baum 179107 2,493,734 1/50 Pearson179114 2,754,373 7/56 Shaper 179114 2,957,954 10/60 Swinehart 1791102,959,645 11/60 Ladd 179107 2,967,913 1/61 Aubert et al 179107 2,975,3893/61 Karg 338--176 2,987,584 6/61 Webber et al 179107 3,025,359 3/62Schilling et al 179110 3,061,689 10/62 McCarrell et al. 179107 ROBERT H.ROSE, Primary Examiner.

STEPHEN W. CAPELLI, Examiner.

